As for conventional centrifugal fans, for example, Japanese Patent Laying-Open No. 5-106591 discloses a sirocco fan for an air blower which aims to improve blowing efficiency (PTL 1). The sirocco fan for an air blower disclosed in PTL 1 is formed such that a plurality of vanes are disposed at regular intervals radially in a ring shape. Each vane is provided with a sub-blade for blowing air introduced from a hollow portion of the sirocco fan.
Japanese Patent Laying-Open No. 2009-28681 discloses an air purifier which aims to increase the circulation efficiency of air flow thereby to significantly increase the effect of improving indoor air environment without increasing air flow rate (PTL 2). The air purifier disclosed in PTL 2 is configured to include an intake for taking in air in a room, an air filter removing dust in the air taken in from the intake, an outlet blowing the air treated by the air filter to the room, and a blower moving the air from the intake to the outlet. A sirocco fan is used for the blower.